'device mem' over from GENERIC to DEFAULTS to be consistent with i386 and
amd64. Additionally, on ia64 enable ACPI by default since ia64 requires
acpi.
reclamation synchronously from get_pv_entry() instead of
asynchronously as part of the page daemon. Additionally, limit the
reclamation to inactive pages unless allocation from the PV entry zone
or reclamation from the inactive queue fails. Previously, reclamation
destroyed mappings to both inactive and active pages. get_pv_entry()
still, however, wakes up the page daemon when reclamation occurs. The
reason being that the page daemon may move some pages from the active
queue to the inactive queue, making some new pages available to future
reclamations.
Print the "reclaiming PV entries" message at most once per minute, but
don't stop printing it after the fifth time. This way, we do not give
the impression that the problem has gone away.
Reviewed by: tegge
current context in the IPI_STOP handler so that we can get accurate stack
traces of threads on other CPUs on these two archs like we do now on i386
and amd64.
Tested on: alpha, sparc64
and increase flexibility to allow various different approaches to be tried
in the future.
- Split struct ithd up into two pieces. struct intr_event holds the list
of interrupt handlers associated with interrupt sources.
struct intr_thread contains the data relative to an interrupt thread.
Currently we still provide a 1:1 relationship of events to threads
with the exception that events only have an associated thread if there
is at least one threaded interrupt handler attached to the event. This
means that on x86 we no longer have 4 bazillion interrupt threads with
no handlers. It also means that interrupt events with only INTR_FAST
handlers no longer have an associated thread either.
- Renamed struct intrhand to struct intr_handler to follow the struct
intr_foo naming convention. This did require renaming the powerpc
MD struct intr_handler to struct ppc_intr_handler.
- INTR_FAST no longer implies INTR_EXCL on all architectures except for
powerpc. This means that multiple INTR_FAST handlers can attach to the
same interrupt and that INTR_FAST and non-INTR_FAST handlers can attach
to the same interrupt. Sharing INTR_FAST handlers may not always be
desirable, but having sio(4) and uhci(4) fight over an IRQ isn't fun
either. Drivers can always still use INTR_EXCL to ask for an interrupt
exclusively. The way this sharing works is that when an interrupt
comes in, all the INTR_FAST handlers are executed first, and if any
threaded handlers exist, the interrupt thread is scheduled afterwards.
This type of layout also makes it possible to investigate using interrupt
filters ala OS X where the filter determines whether or not its companion
threaded handler should run.
- Aside from the INTR_FAST changes above, the impact on MD interrupt code
is mostly just 's/ithread/intr_event/'.
- A new MI ddb command 'show intrs' walks the list of interrupt events
dumping their state. It also has a '/v' verbose switch which dumps
info about all of the handlers attached to each event.
- We currently don't destroy an interrupt thread when the last threaded
handler is removed because it would suck for things like ppbus(8)'s
braindead behavior. The code is present, though, it is just under
#if 0 for now.
- Move the code to actually execute the threaded handlers for an interrrupt
event into a separate function so that ithread_loop() becomes more
readable. Previously this code was all in the middle of ithread_loop()
and indented halfway across the screen.
- Made struct intr_thread private to kern_intr.c and replaced td_ithd
with a thread private flag TDP_ITHREAD.
- In statclock, check curthread against idlethread directly rather than
curthread's proc against idlethread's proc. (Not really related to intr
changes)
Tested on: alpha, amd64, i386, sparc64
Tested on: arm, ia64 (older version of patch by cognet and marcel)
amd64, and is a factor of 3 less than the value previously auto-sized on
a 12GB machine, which would cause an overflow in calculations involving the
maxbcache int, causing bufinit() to loop forever at boot.
Reviewed by: mlaier, peter
changes in MD code are trivial, before this change, trapsignal and
sendsig use discrete parameters, now they uses member fields of
ksiginfo_t structure. For sendsig, this change allows us to pass
POSIX realtime signal value to user code.
2. Remove cpu_thread_siginfo, it is no longer needed because we now always
generate ksiginfo_t data and feed it to libpthread.
3. Add p_sigqueue to proc structure to hold shared signals which were
blocked by all threads in the proc.
4. Add td_sigqueue to thread structure to hold all signals delivered to
thread.
5. i386 and amd64 now return POSIX standard si_code, other arches will
be fixed.
6. In this sigqueue implementation, pending signal set is kept as before,
an extra siginfo list holds additional siginfo_t data for signals.
kernel code uses psignal() still behavior as before, it won't be failed
even under memory pressure, only exception is when deleting a signal,
we should call sigqueue_delete to remove signal from sigqueue but
not SIGDELSET. Current there is no kernel code will deliver a signal
with additional data, so kernel should be as stable as before,
a ksiginfo can carry more information, for example, allow signal to
be delivered but throw away siginfo data if memory is not enough.
SIGKILL and SIGSTOP have fast path in sigqueue_add, because they can
not be caught or masked.
The sigqueue() syscall allows user code to queue a signal to target
process, if resource is unavailable, EAGAIN will be returned as
specification said.
Just before thread exits, signal queue memory will be freed by
sigqueue_flush.
Current, all signals are allowed to be queued, not only realtime signals.
Earlier patch reviewed by: jhb, deischen
Tested on: i386, amd64
variable and returns the previous value of the variable.
Tested on: i386, alpha, sparc64, arm (cognet)
Reviewed by: arch@
Submitted by: cognet (arm)
MFC after: 1 week
This kernel config briefly describes some of the major MAC policies
available on FreeBSD. The hope is that this will raise the awareness
about MAC and get more people interested.
Discussed with: scottl
it to __MINSIGSTKSZ. Define MINSIGSTKSZ in <sys/signal.h>.
This is done in order to use MINSIGSTKSZ for the macro PTHREAD_STACK_MIN
in <pthread.h> (soon <limits.h>) without having to include the whole
<sys/signal.h> header.
Discussed with: bde
archs and enable splash(4) by default (the non-working screen savers
either don't compile or just have no effect when loaded, i.e. don't
cause harm).
MFC after: 1 week
in the arm __swp() and sparc64 casa() and casax() functions is actually
being used as an input and output and not just the value of the register
that points to the memory location. This was the underlying source of
the mbuf refcount problems on sparc64 a while back. For arm this should be
a nop because __swp() has a constraint to clobber all memory which can
probably be removed now.
Reviewed by: alc, cognet
MFC after: 1 week
variables rather than void * variables. This makes it easier and simpler
to get asm constraints and volatile keywords correct.
MFC after: 3 days
Tested on: i386, alpha, sparc64
Compiled on: ia64, powerpc, amd64
Kernel toolchain busted on: arm
address, writting non-canonical address can cause kernel a panic,
by restricting base values to 0..VM_MAXUSER_ADDRESS, ensuring
only canonical values get written to the registers.
Reviewed by: peter, Josepha Koshy < joseph.koshy at gmail dot com >
Approved by: re (scottl)
- Let creator_bitblt() return ENODEV as it's not implemented (missed
in sys/dev/fb/creator.c rev. 1.6).
- As a speed optimization inline the creator_ras_wait() etc. helper
functions and also cache setting the font increment, font width
and plane mask. [1]
- I got the meaning of V_DISPLAY_BLANK wrong, it's blank like turn
off and not blank like turn on and clear the screen. So move
clearing the screen to creator_clear() were it hopefully belongs.
- Properly implement V_DISPLAY_BLANK, V_DISPLAY_STAND_BY and
V_DISPLAY_SUSPEND. This makes blank_saver.ko and green_saver.ko
work. [1]
- Change the order of operations in creator_fill_rect(), i.e. write
y before x and cy before cx. This fixes drawing the top part of
the border with Elite3D cards when switching from Xorg to a VTY.
- Move setting the chip configuration we use and invalidating the
cache variables to creator_set_mode() and set the V_ADP_MODECHANGE
flag. This causes creator_set_mode() to be called when the X server
shuts down which fixes the screen corruption caused most of the
time by Xorg not restoring the original configuration present at
startup.
Inspired by/based on: Xorg [1]
Approved by: re (scottl)
psm(4), ukbd(4), ums(4) and usb(4) on by default. Modulo some nits with
the most annoying one probably being USB keyboards no longer working at
the OFW boot prompt after halting FreeBSD these drivers work fine on
sparc64 including X and there's nothing left that I'd consider a show-
stopper. I.e. graphical consoles on sun4u machines should either work
out of the box or by plugging in a card that is supported by either
creator(4) or machfb(4). The exception obviously are SBus-only machines
without UPA slots like some Ultra 1 (but which also still lack support
in other areas) and certain Exx0 (but which probably are mainly used
with serial consoles anyway). I'll try to add a cgsix(4) for these later
as Sun CG6 cards are probably the most common SBus framebuffer cards in
sun4u machines. I however don't see much sense in adding drivers for the
dozen of SBus framebuffers that were destined for sparc v8 machines.
The rest of the USB drivers aren't enabled as I'm only aware of ukbd(4)
and ums(4) as well as ohci(4) working with the on-board ALI M5237 and
Sun PCIO-2 controllers. Aue(4) definitely doesn't work on sparc64, yet.
Thanks to:
- Jake for the initial work on syscons(4) on sparc64 and creator(4).
- Marcel for uart(4) and especially for its support for the SCCs which
are only used on sparc64 so far. In various regards it wouldn't have
been possible to enable syscons(4) by default on sparc64, yet, without
uart(4).
- All that tested patches.
Ok'ed by: scottl (RE hat), tmm
vm_page's machine-dependent fields. Use this function in
vm_pageq_add_new_page() so that the vm_page's machine-dependent and
machine-independent fields are initialized at the same time.
Remove code from pmap_init() for initializing the vm_page's
machine-dependent fields.
Remove stale comments from pmap_init().
Eliminate the Boolean variable pmap_initialized from the alpha, amd64,
i386, and ia64 pmap implementations. Its use is no longer required
because of the above changes and earlier changes that result in physical
memory that is being mapped at initialization time being mapped without
pv entries.
Tested by: cognet, kensmith, marcel
- Implement sampling modes and logging support in hwpmc(4).
- Separate MI and MD parts of hwpmc(4) and allow sharing of
PMC implementations across different architectures.
Add support for P4 (EMT64) style PMCs to the amd64 code.
- New pmcstat(8) options: -E (exit time counts) -W (counts
every context switch), -R (print log file).
- pmc(3) API changes, improve our ability to keep ABI compatibility
in the future. Add more 'alias' names for commonly used events.
- bug fixes & documentation.
mutex instead of a MTX_DEF one in order to defer preemption while
reading the date and time registers. If we don't manage to read them
within the time slot where we are guaranteed that no updates occur we
might actually read them during an update in which case the output is
undefined.
the number of registered adapters instead of determining again whether
stdout is a supported card (and which might have failed to attach and
register).
- Drop creator_set_mode() and move the relevant parts to creator_fill_rect()
and creator_putc() respectively. This is a bit cleaner than having to
make sure that creator_set_mode() was called before creator_fill_rect()
or creator_putc() are used and matches better what Xorg does.
- Fix a bug in the handling of the FBIOSCURSOR IOCTL; the code was meant
to return ENODEV for all invocations expect when used to disable the
cursor and not just when used for enabling the cursor.
- In case the adapter is the OFW stdout move its OFW cursor to the start
of the last line on halt so OFW output doesn't get intermixed with what
FreeBSD left on the screen. With hindsight this is what the faking of a
hardware cursor which was removed in the last revision really was about,
i.e. to keep the OFW updated about the current cursor position. The new
approach however is simpler while producing the same result and doesn't
cause the first letter of the OFW output to be turned into a blank and
a newline.
- Add variable names to the prototypes of creator_cursor_*() which were
added in the last revision and list them alphabetically in order to match
the style of this file.
for the SYS_RES_IOPORT -> SYS_RES_MEMORY transition again. While it
was helpful to not need to change all of the affected drivers in a
single pass together with ebus(4) we probably shouldn't start into
6.0 with such a hack.
This requires some of the modules of affected drivers to be rebuilt,
namely: auxio(4), snd_audiocs(4) and puc(4).
by default, yet.
- Replace "graphics cards" with "framebuffers" in the description
of creator(4) in order to make it uniform with the description of
machfb(4) and the latter occur both on-board and as add-on cards.
- Use register macros instead of magic values in the code. [1]
- Check the return values of OF_getprop() and other stuff that actually
can fail.
- Let the unimplemented video driver methods return ENODEV rather
than 0 so other code isn't tricked into thinking a certain operation
was successfull. In case of e.g. the video driver creator_ioctl()
this caused vidcontrol(1) to return random garbage information.
Remove the TODO macros in the unimplemented video driver methods
which did a printf("%s: unimplemented\n", __func__). Under certain
circumstances these managed to invoke a printf() when a low-level
console device wasn't attached, yet, causing a Fast Data Access MMU
Miss. These macros were only really usefull for development anyway.
- Set the struct video_adapter and struct video_info va_flags and
vi_flags etc. as appropriate.
- In creator_configure() don't rely on hitting the node which is the
chosen console device first when searching the OFW tree for adapters
compatible with this driver. Instead just check whether the chosen
console device is a viable target for this driver. Targets that are
not the console (including additional cards in multi-head configs)
will be attached through creator_upa_attach(). I think this how the
code in creator_configure() was actually meant to work.
Honour the VIO_PROBE_ONLY flag and don't initialise and register the
console device twice when creator_configure() is called a second time
during sc_probe_unit().
Let creator_configure() return the number of the found adapters,
i.e. 1 in case probing succeeds, as it's expected. The return values
of video adapter configure functions however currently aren't checked
so this doesn't make a difference at the moment.
- In creator_upa_attach() don't rely on probing and attaching the
adapter which is the console first, in case there are multiple
adpaters and one of them is the console this could lead into using
the video adapter unit 0 twice.
- Make the check for DACs with inverted cursor control a bit more
precise and actually honour that information when turning the cursor
on or off. Add a helper function creator_cursor_enable() for this
in order to keep code duplication low. [1]
- Don't bother with faking a hardware cursor in case a device is the
console. Apparently this was meant to start kernel output right after
where the firmware left. In general this isn't worth the fuzz and
also had no real effect as creator_set_mode() did clear the screen
in any case, not just in case a device was not the console.
- Implement creator_fill_rect() and use it to actually blank the
display in creator_blank_display() when the mode is V_DISPLAY_BLANK,
moving blanking the display out of creator_set_mode(). Use it also
to implement creator_set_border() so the border can be re-drawn
when switching to a VTY from X, exiting X, etc. (which leaves us
with a black border most of the time).
- Implement the video driver creator_ioctl(), moving the implementation
of the IOCTL interface from the fbN CDEV version of creator_ioctl()
into the video driver version and use the latter to implement the
former. Use fb_commonioctl() to handle most of the FBIO IOCTLs.
This gives programs like vidcontrol(1) which use the video driver
creator_ioctl() a chance of working.
Implement turning off the cursor via the FBIOSCURSOR IOCTL, which
Xorg uses to in order to inform the OS that it's taking over the
cursor. In creator_putm() check whether the cursor is enabled and
(re-)install it if necessary, moving installing the cursor out of
creator_init() and into a helper function creator_cursor_install().
This fixes the missing mouse pointer when switching to a VTY from X,
exiting X, etc.
- Some clean-up (remove unused/useless code, etc.).
o sparc64/creator/creator_upa.c / sparc64/sparc64/sc_machdep.c:
- Attach syscons(4) as an own pseudo-device on the nexus rather than
directly in creator_upa_attach(), similiar to attaching syscons(4)
as a pseudo-device on isa(4) on other archs. This makes it a whole
lot easier to do the right thing in multi-head configs, especially
with different types of graphics adapters. [2]
- Set SC_AUTODETECT_KBD by default so USB keyboards work out of the
box. [2]
Based on/obtained from: Xorg 'ffb' driver [1]
Based on/obtained from: FreeBSD/powerpc [2]
Use bus_generic_probe() and add a bus_add_child() interface method to
allow device drivers to use the identify method to add themselves if
need be (e.g. syscons(4)).
- Use FBSDID.
consist of the expected number of address and size cells (we can't use
dynamic arrays here because at the point in the boot process when this
code is used malloc() doesn't work, yet). This fixes a Fast Data Access
MMU Miss when uart(4) (erroneously) calls OF_decode_addr() to decode
the address of PS/2 keyboards. PS/2 keyboards use a different and also
undocumented scheme at the first parent node than mapping at 'ranges'
properties. It's however not worth implementing that other scheme and
actually also fits atkbdc(4) better to just start at the first parent
node of PS/2 keyboards which is the 8042 controller (I have atkbdc(4)
working that way).
- Use FBSDID.
MFC after: 1 month
- Add locking.
- Account for if the MC146818_NO_CENT_ADJUST flag is set we don't need
to check wheter year < POSIX_BASE_YEAR.
- Add some comments about mapping the day of week from the range the
generic clock code uses to the range the chip uses and which I meant
to add in the initial version.
- Minor clean-up, use __func__ instead of hardcoded function names in
error strings.
o in the rtc(4) front-end additionally:
- Don't leak resources in case mc146818_attach() fails.
- Account for ebus(4) defaulting to SYS_RES_MEMORY for the memory
resources since ebus.c rev. 1.22.
- Add support for storing the century in MK48TXX_WDAY_CB on MK48Txx with
extended registers when the MK48TXX_NO_CENT_ADJUST flag is set (and which
is termed somewhat confusing as it actually means don't manually adjust
the century in the driver).
- Add the MI part of interfacing the watchdog functionality of MK48Txx with
extended registers with watchdog(9). This is inspired by the SunOS/Solaris
drivers for the 'eeprom' devices also having watchdog support. I actually
expected this to work out of the box on Sun Exx00 machines with 'eeprom'
devices which have a 'watchdog-enable' property. On terminal count of the
the watchdog timer however only the MK48TXX_FLAGS_WDF bit rises but the
reset signal and the interrupt respectively (depending on whether the
MK48TXX_WDOG_WDS bit of the chip and the MK48TXX_WDOG_ENABLE_WDS flag
of the driver respectively is set) goes nowhere. Apparently passing the
reset signal on to the WDR line of the CPUs has to be enabled somewhere
else but we don't have documentation for the Exx00 specific controllers.
I decided to commit this nevertheless so it can be enabled in the eeprom(4)
front-end later in e.g. 6.0-STABLE without breaking the API. Besides the
Exx00 the watchdog part of the MK48Txx should also work on E250 and E450.
Possibly also without extra fiddling on these machines but I haven't
found someone willing to give it a try on such a machine so far.
- Use uintXX_t instead of u_intXX_t, use __func__ instead of hardcoded
function names in error strings.
eeprom_ebus_attach() and eeprom_sbus_attach() into eeprom_attach()
respectively. Since the introduction of the ofw_bus interface some
time ago and now that ebus(4) also uses SYS_RES_MEMORY for the
memory resources since ebus.c rev. 1.22 there is no longer a
need to have separate front-ends for ebus(4), fhc(4) and sbus(4).
- Fail gracefully instead of panicing when the model can't be
determined.
- Don't leak resources when mk48txx_attach() fails.
- Use FBSDID.
compatibility with ISA devices while in fact all known EBus devices
actually use memory space turned out to be not a good idea as so far
there is only the 'rtc' device known to show up either on an EBus or
ISA bus but not on any of the other busses used on sparc64. However
there are quite a couple of them that show up on either EBus, FireHose
or SBus. In order to save extra code in the respective drivers switch
ebus(4) to actually use SYS_RES_MEMORY for the memory resources of
its children. At least for transition still accept SYS_RES_IOPORT
and silently change it to SYS_RES_MEMORY. [1]
- In ebus_probe() use ofw_bus_get_name() instead of re-implementing it
via ofw_bus_get_node() and OF_getprop().
- Remove some unused variables.
- Use FBSDID.
Discussed with: tmm (some time ago)
the iteration variable as the RID when adding the respective resource
to the child via bus_set_resource(). In case a device has both I/O
and memory resources this generates gaps in the newbus resources of
the child, e.g. its first memory resource might end up as RID 1.
To solve this mimic resource_list_add_next() via resource_list_find()
and bus_set_resource(); we can't just use resource_list_add_next()
here as this would circumvent the limit checks in isa_set_resource()
of the common ISA code.
This however is more or less a theoretical problem so far as all known
ISA devices on sparc64 soley use I/O space.
- Just use bus_generic_rl_release_resource() for isa_release_resource()
instead of re-implementing the former.
- Improve some comments to better reflect reality, minor clean-up and
simplifications, return NULL instead of 0 were appropriate.
front-end and the LSI64854 and NCR53C9x code in case one of these
functions fails. Add detach functions to these parts and make esp(4)
detachable.
- Revert rev. 1.7 of esp_sbus.c, since rev. 1.34 of sbus.c the clockfreq
IVAR defaults to the per-child values.
- Merge ncr53c9x.c rev. 1.111 from NetBSD (partial):
On reset, clear state flags and the msgout queue.
In NetBSD code to notify the upper layer (i.e. CAM in FreeBSD) on reset
was also added with this revision. This is believed to be not necessary
in FreeBSD and was not merged.
This makes ncr53c9x.c to be in sync with NetBSD up to rev. 1.114.
- Conditionalize the LSI64854 support on sbus(4) only instead of sbus(4)
and esp(4) as it's also required for the 'dma', 'espdma' and 'ledma'
busses/devices as well as the 'SUNW,bpp' device (printer port) which
all hang off of sbus(4).
- Add a driver for the 'dma', 'espdma' and 'ledma' (pseudo-)busses/
devices. These busses and devices actually represent the LSI64854 DMA
engines for the ESP SCSI and LANCE Ethernet controllers found on the
SBus of Ultra 1 and SBus add-on cards. With 'espdma' and 'ledma' the
'esp' and 'le' devices hang off of the respective DMA bus instead of
directly from the SBus. The 'dma' devices are either also used in this
manner or on some add-on cards also as a companion device to an 'esp'
device which also hangs off directly from the SBus. With the latter
variant it's a bit tricky to glue the DMA engine to the core logic of
the respective 'esp' device. With rev. 1.35 of sbus.c we are however
guaranteed that such a 'dma' device is probed before the respective
'esp' device which simplifies things a lot. [1]
- In the esp(4) SBus front-end read the part-unique ID code of Fast-SCSI
capable chips the right way. This fixes erroneously detecting some
chips as FAS366 when in fact they are not. Add explicit checks for the
FAS100A, FAS216 and FAS236 variants instead treating all of these as
ESP200. That way we can correctly set the respective Fast-SCSI config
bits instead of driving them out of specs. This includes adding the
FAS100A and FAS236 variants to the NCR53C9x core code. We probably
still subsume some chip variants as ESP200 while in fact they are
another variant which however shouldn't really matter as this will
only happen when these chips are driven at 25MHz or less which implies
not being able to run Fast-SCSI. [3]
- Add a workaround to the NCR53C9x interrupt handler which ignores the
stray interrupt generated by FAS100A when doing path inquiry during
boot and which otherwiese would trigger a panic.
- Add support for the 'esp' devices hanging off of a 'dma' or 'espdma'
busses or which are companions of 'dma' devices to esp(4). In case of
the variants that hang off of a DMA device this is a bit hackish as
esp(4) then directly uses the softc of the respective parent to talk
to the DMA engine. It might make sense to add an interface for this
in order to implement this in a cleaner way however it's not yet clear
how the requirements for the LANCE Ethernet controllers are and the
hack works for now. [2]
This effectively adds support for the onboard SCSI controller in
Ultra 1 as well as most of the ESP-based SBus add-on cards to esp(4).
With this the code for supporting the Performance Technologies SBS430
SBus SCSI add-on cards is also largely in place the remaining bits
were however omitted as it's unclear from the NetBSD how to couple
the DMA engine and the core logic together for these cards.
Obtained from: OpenBSD [1]
Obtained from: NetBSD [2]
Clue from: BSD/OS [3]
Reviewed by: scottl (earlier version)
Tested with: FSBE/S add-on card (FAS236), SSHA add-on card (ESP100A),
Ultra 1 (onboard FAS100A), Ultra 2 (onboard FAS366)
device and which also applies to the children. This is very usefull for
drivers for the various subordinate busses so they don't need to fiddle
with the OFW node of their parent themselves. As SBus busses hang of the
nexus and we don't use the ofw_bus interface for nexus devices, yet, this
would also require special knowledge about this in the drivers for the
SBus children which these shouldn't need to have.
This includes switching to use an unshifted IGN in the sc_ign member of
the sbus(4) softc internally.
- For SBus child devices where there are variants that are actually split
split into two SBus devices (as opposed to the first half of the device
being a SBus device and the second half hanging off of the first one)
like 'auxio' and 'SUNW,fdtwo' or 'dma' and 'esp' probe the SBus device
which is a prerequisite to the driver attaching to the second one with
a lower order. This saves us from dealing with different probe orders
in the respective device drivers which generally is more hackish.
- Remove a stale comment about the 'specials' array above the attaching
of the child devices. This is a remnant of the NetBSD/sparc origin of
this code. There the 'specials' array is also used to probe certain
devices which are prerequisites to others first. Why NetBSD soley
relies on the devices having the expected order in the OFW tree on
sparc64 isn't clear to me, as far as I can tell OFW doesn't guaranteed
such things.
